This invention relates to a structural mat matrix such as a roofing shingle mat matrix.
For many years, structural articles such as roofing shingles have been comprised of fiberglass substrates coated with a binder which bonds together the fiberglass substrate fibers. Such substrates are nonwoven fiberglass mats which are desirable because they are lighter in weight than previously used mats. Fiberglass mats have also been preferred as roofing shingle substrates because of their fire resistant nature, their resistance to moisture damage, their excellent dimensional stability, their resistance to curl with temperature changes, their resistance to rot and decay, and their ability to accept more highly filled asphalt coatings.
Heretofore, efforts to optimize fiberglass roofing shingle substrates have focused on attempts at improving their tear strength and tensile strength without unduly increasing the weight of the shingle. Heavier shingles and other structural articles are generally more expensive because of greater raw material and transportation costs. Operating within such weight/cost constraints, shingle manufacturers have found that, to improve tear strength, they had to sacrifice tensile strength and vice versa.
U.S. Pat. No. 4,112,174 discloses a mat suitable in the manufacture of roofing products which includes monofilament glass fibers, glass fiber bundles and a relatively small amount of binder, e.g. binder which is 15% by dry weight of the mat. The mat has a weight of between approximately 2.00 and 2.40 lbs/100 square feet. U.S. Pat. No. 4,242,404 discloses a glass fiber mat useful for roofing products which includes individual filament glass fibers and extended glass fiber elements and a binder applied in an amount of about 3% to 45% by weight of the finished mat. The basis weight of the finished mat is described as being at least 1 lb./100 sq. ft and preferably about 2.0 to 3.0 lbs/sq. ft.
U.S. Pat. No. 4,472,243 discloses sheet type roofing material for use in built-up roofing and in the manufacture of roofing shingles. Chopped glass fibers are dispersed in a slurry of cellulosic fibers and binder is added. According to the patent, the material comprises 10-60 wt % glass fibers of varying lengths, 15-80% wt % cellulosic fiber and 5-25% binder. The patent states that the proportions and sizes of cellulosic and glass fibers described therein "provide the desired balance of structural properties" in the material to render it "suitable as substrate for roofing material" to "meet the desired standards for mechanical strength and fire resistance." The patent further notes that the "[g]lass fiber content of the felt of the invention is important in controlling its porosity and skeletal structure. On the high end of glass fiber content the felt substrate tends to be porous with a high order of skeletal structure. Such a felt will uncontrollably absorb excessive amounts of asphaltic saturant at a very high rate during roofing shingle processing and this has a deleterious effect in the spread of flame test due to severe asphaltic filled coating slides."
Surprisingly, the applicant has found that by producing a mat having a relatively high fiberglass content and relatively low cellulosic component and binder contents, the mat matrix has the same physical properties (such as tensile strength) of more costly heavy weight mats, with substantially increased tear strength.